Reed relay



United States Patent O 3,132,226 REED RELAY Robert Lee Pech, ltr., NewYorlr, NX., assigner to Bell Telephone Laboratories, Incorporated, NewYork, NY., a corporation of New York Filed May 15, 1961, Ser. No.110,681 d Claims. (Cl. 317-137) This invention relates to circuitcontrolling devices and more particularly to magnetically operableswitching devices including a remanent magnetic control member.

In general it is a desideratum of switching systems of the typeemployed, for example, to interconnect selectively and in variouscombinations the particular input stations in a communications network,that they be responsive to current pulses of very short duration andhaving a minimal separation in time, such as those commonly employed inelectronic control circuits. It is well known that the use in telephonesystems of switching relays having these desired characteristics canprovide improved telephone service as well as economy of installationand operation. Relays responsive to short energizing pulses aredisclosed in copending patent applications Serial No. 824,222 of A.Feiner et al., iiled July l, 1959, now Patent No. 2,995,637, Serial No.824,225 of l. A. Baldwin et al., filed luly l, 1959, new Patent No.3,002,- 067, and Serial No. 847,919 of R. L. Peek, Ir., led Gctober 22,1959, now Patent No. 3,059,075.

The electronically operable relays described in the above-namedapplications employ remanent magnetic control members to provide themagnetic eld which actually operates the contacts or" a reed switch. Thecontrol men ber is characterized by a substantial magnetic retentivity,so that after the cessation of a short pulse applied to a control coilit remains in one of its plurality of stable magnetization states. lt isapparent that successful operation of such devices is criticallydependent on the establishlnent of the requisite remanent magnetizationstates by the energizing pulse. Due to the compactness of many suchrelays, however, it is often the case that the magnetic field of thecontrol coil encompassing one remanent member is suiiiciently strong toaffect the magnetic state of another remanent member, even though thesecond member be strongly biased by a permanent magnet. The stray fieldmay in some instances be sumcient to cause a reversal of the desiredrelay action.

Relays have been built employing remanent magnetic control members andproviding nonmarginal positive action of the switch contacts in both theoperate and release functions. By positive action is meant theoperati-on or release of the relay contacts under the iniiuence of theelectrically controllable eld of the remanent magnetic members ratherthan mechanically by the spring tension of one or both of the contacts.By nonmarginal operate or release is meant the independence of the relayaction of the magnitude of the control pulses, provided the energy ofsuch pulses exceeds a certain minimum value. One such nonmarginalpositive action relay is disclosed in my aforementioned copendingapplication Serial No. 847,919 and comprises a pair of remanentlymagnetic control members and a pair of control windings individuallyassociated therewith. A device of this type is inherently nonpolar,i.e., the switching action is dependent,

'not on the polarity of a single control pulse, but on the relativepolarities of the pulses applied to the two windings. in some switchingnetworks, however, it is desirable to employ nonmarginal positive actionrelays having polarized characteristics.

Accordingly, it is .an object of this invention to provide anelectrically operable polarized locking relay having ICC nonmarginalpositive action in both the operate and the release functions.

It is also an object of this invention to improve the operatingcharacteristics of relays of this type.

An additional object of the invention is to provide an electricallyoperable polarized transfer relay having nonmarginal positive action.

A further object of the invention is to provide a coordinate switchingmatrix in which positive nonmarginal operate and release of anycrosspoint may be achieved independently of the status of the othercrosspoints in the array.

These and other objects of the invention are achieved in a specificillustrative embodiment thereof comprising a reed switch having a pairof magnetically operable contacts, a pair of .magnetically retentivecontrol members, a pair of control windings individually associated withthe control members, and a diode or other rectifying means.

it is a feature of the invention that the control windings are adaptedto produce opposing magnetic fields of substantially equal magnitudeswhen energized by currents of like polarity.

Another feature of the invention is that the control windings areserially connected.

lt is a further feature of the invention that the diode is connected inparallel with one of the control windings, thereby providing a shuntpath around that winding for currents of one polarity.

The reed switch contacts of the illustrative embodiment are operated bya short current pulse of the polarity which flows through one of thecontrol windings and through the diode shunt path around the `secondcontrol winding. The switch contacts are released by an elcctroniccurrent pulse of opposite polarity which passes serially through bothcontrol windings, thereby generating opposing magnetic ields of likeintensity.

The mode of operation as well as the above-mentioned and other objectsand features of the invention will be better understood from thefollowing more detailed discussion taken in conjunction with theaccompanying drawing in which:

FIG. l depicts one specific embodiment of the invention;

FIG. 2 depicts a transfer relay embodying the principles of theinvention; and

FIG. 3 depicts schematically a switching matrix in accordance with theprinciples of the invention.

Turning now to the drawing, there is shown in FIG. 1 a reed switchhaving an envelope 1t), as of glass, with terminals 11 sealed into theopposite ends thereof. Reeds 12 and 13, which in the illustrativeembodiment function as control members in addition to acting as switchcontacts, are of a material characterized by a plurality of stableremanent magnetization states, and are attached to the terminals lli sothat their free ends overlap near the center of envelope 1?. Reeds 12and 13 are separately encompassed by control windings 16 and 17,respectively. A soft magnetic shunt member 19, snown in schematic form,is situated adjacent the envelope l@ in the region where the free endsof the renranent reeds 12 and 13 overlap.

The coils 16 and 17 are wound and connected so that when both areenergized by currents of like polarity the magnetic fields producedalong the axis of the envelope 1t) are in opposition. More specifically,the control coils 16 and i7 in the illustrative embodiment shown in FIG.l are oppositely wound and serially connected. In accordance with theinvention a diode i8 is connected in parallel with the coil 17, therebyforming a shunt path around the coil 17 for currents of one polarity.More aisance el? particularly, the diode lli in FlG. l forms a shuntpath for positive currents. Thus, negative currents applied to thecontrol circuit flow through both windings lo and 17, while positivecurrents flow through winding lo but Vare shunted around winding .7.

in accordance with one feature of the invention the control windings lloand 17 are adapted to produce opposing magnetic lields of substantiallyequal magnitude. While it is not necessary that the intensities of thetwo fields be exactly equal, there is a definite limit to the ditferencewhich may exist between them. The limit on the differential which isconsistent with the invention is determined principally by the geometryof the relay. That is, the difference must be less than the magnitude ofthe field of either coil which is just suficient to switch the magneticstate of the free end of reed encompassed by the other. If it be assumedthat the forward resistance of the diode ld is zero while the reverseresistance is infinite, then the number of turns in the coil lo is, m stadvantageously, equal to the number in the coil 17. lf necessary, thedeparture of the diode from this ideal may be compensated by anappropriate diiierence in the turns ot each coil. Equivalently, thepositions of the coils lr6 and i7 may be axially shited with respect tothe reeds l2 and 13 so that the overlapping contact portions thereofcoincide with the region in which the opposing magnetic fieldselectively cancel each other. Thus, when both coils are energized,thereby magnetizing the control members, like magnetic poles of similarstrengths are produced at the free ends ofthe reeds.

When a control current pulse ot negative polarity is applied to theembodiment of FIG. l, axially opposing magnetic fields are produced bythe windings lo rrnd llf. The axial magnetic lield within the coil lomagnetizes the reed l2 so that the free end thereof becomes a magneticnorth pole. Similarly, the free end of the reed t3 is magnetized by theaxial iieldrof the winding i7 so that its free end is a magnetic northpole. Due to the magnetic retentivity of the reeds l?. and 13, eachremains in a stable state of remanent magnetization after the currentceases. Since their overlapping free ends are of like magnetic polarityrthey repel each other and the switch contacts assume the open orreleased condition.

When a control current pulse of positive polarity is applied to theembodiment depicted in FlG. l an axial magnetic held is produced bywinding lo, while no field is produced by winding ll, which is shuntedby diode 1S. The field of winding lo magnetizes the reed :l2 so that itsfree end becomes a magnetic south pole. The iield of coil winding i6will also tend to remagnetize the reed 13 in the sense of its existingmagnetization, so that at the end of the pulse this existingmagnetization is either unchanged or slightly increased. Due to itsmagnetic retentivity, the reed l2 assumes a stable state of remanentmagnetization of the same sense as the existing magnetization of thereed i3. Thus, the overlapping tree ends of the reeds 12 and 13 are ofmagnetically opposite polarity and the switch contacts assume the closedor operated condition.

It canibe seen from the above explanation that both the operate andrelease actions of a relay in accordance with the invention arenomarginal. That is, while there is a current pulse amplitude belowwhich the condition of the switch contacts will not be changed, thecontrol pulse may exceed this amplitude by any amount without causing areversal of the change produced initially. This is so because when arelease pulse is appliedto the control circuit to magnetize the reeds inopposition, the same amount of current llows through both coils lo andl. Since the opposing magnetic fields are of substantially equalintensity, it is not possible for the rield of one coil to affect themagnetizationV state of the reed encompassed by the other coil. instead,the :flux lines of the opposing elds complete a magnetic circuit byflowing through the sott magnetic shunt member i9, and thence through anair return path or through a return path member not Vv'l en the currentexceeds a certain amount the remanent magnetic state ot Vthe reed l?. isswitched and the free ends of the reeds close due to mutual magneticattraction of unlike poles. It the magnetic lield is in excess of theminimum required to operate the contacts, the operate action is evenmore positive. The magnetic flux lines produced by the current in coillo liow through both reeds to complete the magnetic circuit, so that thestrength of the unlike poles at the overlapping free ends ofthe reeds l2and l is increased.

Eoth the operate and release actions of a relay embodying the inventionare positive. That is, the opening and closing of the switch contacts iseliected by the mutual attraction or repulsion of the magnetic poles atthe juxtaposed free ends ot the reeds and not by theV mechanicalstiffness of the reeds. Furthermore, because ol the remanentmagnetization of the reeds in the embodiol El@ l, the contacts remainlocked in either the operated or released condition after the cessationof the control current.

ln FlG. 2 there is shown a transfer relay in accordance withtheinvention and comprising two reed switches of the type described above.is individually encompassed by one of two control windings while asingle control winding encompasses the other reed of each pair. Morespecifically, reeds 22 and 215iare encompassed Vby control coils 27 and28, respectively, while reeds 2.3 and 26 are both encompassed by coil29.

Coil 27 is connected in 'series with coil 2S which in turn is connectedin series with coil 29. Coils 27 and 2h are so wound and connected that,were the same current to iiow through both of them they would produceoppositely directed axial fields. However, diode 3l is connected inparallel with coil 227, providing a shunt path therearound for negativecurrents. ln like manner, diode 32 is connected in parallel with coil2.8, providing a shunt path therearound for positive currents.

When a negative current is applied to the control circuit of theembodiment shown in FIG. 2, it liows around coil 27 through'the shuntingdiode 3l, through coils 28 and Z9 which produce oppositely directedaxial magnetic iields. The remanent reeds 2d and 26 are oppositelymagnetized by the opposing fields so that the free ends thereof becomemagnetic north poles. As like poles repel each other the reed contactsare released. However, that part of the field produced by coil Z9 whichacts on reed 23 is unopposed since no current liows in coil 27.Therefore, the remanent magnetization of reed 22 is. reenforced and,reeds 22 and 23 being magnetized in the same direction, their free endsare opposite magnetic poles. The switch contacts are thus closed bymagnetic force.

When a positive current is applied to the control circuit coils 2! and29 are energized while coil 2S is shunted by the diode 32. The axialields of the energized coils are oppositely directed so that reeds 22and 23 develop like magnetic poles at their free ends. Thus thepreviously closed contacts are opened. Conversely, that portion of thefield of coil 29 acting on reed 26 is unopposed so that the tree ends ofreeds and 26 develop unlike magnetic poles. The previously openedcontacts are, therefore, closed.

lt will be appreciated that, as in the embodiment shown in FIG. l, thetransfer relay depicted in FL'G. 2 is polarized, and is characterizedbyV positive, nonmarginal action in both the operate'and releasefunctions. Thus, all the advantages of the single contact-pair relay areretained in the transfer relay.

if a plurality of clays embodying the invention are assembled in acoordinate switching matrix, a particularly advantageous mode ofoperation may be realized. In par- Cne reed of each switch ticular, aplurality of relays of the type shown in FIG. 1 may be arranged in acoordinate switching matrix as illustrated in FIG. 3, in whichcorresponding parts are designated by the same reference with subscriptsappropriate tothe coordinates of the crosspoint. One end of the controlcircuit of each relay is connected to a horizontal or H lead, while theother end is connected, through a current blocking diode 40, to avertical or V lead. In addition, each shunting diode 1% is connected toa second vertical or V lead.

Application of a negative potential to a V2 lead and ground to an H leadoperates the crosspoint of these two leads and that crosspoint only.Application of a positive potential to a V lead and ground to an H leadreleases the crosspoint of these two leads and that crosspoint only. Thecurrent blocking diodes, designated by reference numeral 40 withappropriate subscripts, prevent current flow in undersired paths betweenthe H and V leads. Thus, coincident operate and release of anycrosspoint in the array may be achieved Without affecting the status ofany other crosspoint in the array. Y

While the illustrative embodiments of the invention have been depictedin the drawings with soft magnetic shunt members, indicated by referencenumeral 19, these are optional and may be omitted if desired.Furthermore, while the embodiments shown in the drawing comprisemagnetically retentive reeds which function as control membersresponsive to short control pulses, it will be appreciated that softmagnetic reeds may be utilized in conjunction with external magneticallyretentive control members. For example, the control members may comprisemagnetically retentive sleeves surrounding the reeds as shown in UnitedStates Patent 2,877,316 of R. L. Peek, Ir. These sleeves may bemagnetized in aiding or opposing senses in the same way as the reedsshown in the drawings, and will then produce either aiding or opposingfields in the reeds which they enclose, so that these reeds will makecontact with aiding fields, and open their contact when the fields areopposing. Other variations of the invention are possible and may be madeby those skilled in the art without departing from its scope and spirit.

What is claimed is:

1. A polar locking relay having positive nonmarginal operate and releaseaction, comprising a reed switch unit having a pair of remanent magneticcontrol members, a rst control coil encompassing one of said controlmembers, a second control coil encompassing the other of said controlmembers, said coils being serially connected and adapted to producesubstantially equal but oppositely directed magnetic fields whenenergized by a control current, and asymmetrically conducting meansconnected in parallel with one of said coils.

2. A relay as in claim l wherein said remanent magnetic control memberscomprise the reeds of said reed switch unit.

3. A relay as in claim 1 wherein said control members comprise a pair ofremanent magnetic sleeves individually encompassing the reeds of saidreed switch unit.

4. A polar locking relay having positive nonmarginal operate and releaseactions, comprising a reed switch unit having tir-st and second remanentmagnetic reed members cantilevered from opposite ends thereof, said reedmembers having juxtaposed Contact portions near the center of said unit,a iirst control coil encompassing one of said reed members, a secondcontrol coil encompassing the other of said reed members, said controlcoils being connected in series and adapted to produce oppositelydirected magnetic iields of substantially equal intensity when energizedby a control current, and asymmetrically conducting means connected inparallel with one of said control coils.

5. A polar locking transfer relay having positive nonmarginal operateand release actions, comprising first and second reed switch units eachhaving a pair of remanent magnetic control members, a iirst control coilencompassing one control member of said irst switch, a second controlcoil encompassing one control member of said second switch, a thirdcontrol coil encompassing the other control member of said first switchand of said second switch, rst and second asymmetrically conductingmeans connected in parallel with said first and second control coils,respectively, said nst asymmetrically conducting means providing a shuntpath around said first coil for currents of one polarity, said secondasymmetrically conducting means providing a shunt path around saidsecond coil for currents of the other polarity, said iirst, second andthird coils being connected in series, said irst coil being adapted toproduce a magnetic eld opposing that of said third coil when energizedby control currents of one polarity and said second coil being adaptedto produce a magnetic iield opposing that of said third coil whenenergized by control currents of the other polarity, the magnitudes ofsaid opposing magnetic eld being substantially equal.

6. A polar locking transfer relay as in claim 5 Wherein said remanentmagnetic control members comprise the reeds of said switch units.

7. A polar locking transfer relay as in claim 5 wherein said controlmembers comprise remanent magnetic sleeves individually encompassing thereeds of said switch units.

8. A coordinate control switching matrix comprising a plurality ofhorizontal conducto-rs, a plurality of pairs of vertical conductors, anda plurality of switches at the crosspoints thereof, each switchcomprising a reed switch unit having a pair of remanent magnetic controlmembers, a ii-rst control coil encompassing one of said members, asecond control coil encompassing tbe other of said members, said coilsbeing serially connected and adapted to produce substantially equal butoppositely directed magnetic fields when energized by a control current,means including a irst asymmetrically conducting means connecting saidrst coil to one vertical conductor at the crosspoint, means connectingsaid second coil to the horizontal conductor at the crosspoint, andmeans including a second asymmetrically conducting means connecting saidiirst and second coils to the other ot' said vertical conductors at thecrosspoint.

References Cited by the Examiner UNITED STATES PATENTS 2,517.9,1 18ll/SO Tschumi 317-150 X 3,005,072 10/61 Brown 31"7`-155.5 X 3,029,3694/62 Lang et al. 317-137 X SAMUEL BERNSTEIN, Primary Examiner.

1. A POLAR LOCKING RELAY HAVING POSITIVE NONMARGINAL OPERATE AND RELEASEACTION, COMPRISING A REED SWITCH UNIT HAVING A PAIR OF REMANENT MAGNETICCONTROL MEMBERS, A FIRST CONTROL COIL ENCOMPASSING ONE OF SAID CONTROLMEMBERS, A SECOND CONTROL COIL ENCOMPASSING THE OTHER OF SAID CONTROLMEMBERS, SAID COILS BEING SERIALLY CONNECTED AND ADAPTED TO PRODUCESUBSTANTIALLY EQUAL BUT OPPOSITELY DIRECTED MAGNETIC FIELDS WHENENERGIZED BY A CONTROL CURRENT, AND ASYMMETRICALLY CONDUCTING MEANSCONNECTED IN PARALLEL WITH ONE OF SAID COILS.